Codeforces Round #248 (Div. 2) A题_html/css_WEB-ITnose

Title link: http://codeforces.com/contest/433/problem/A

Tips: A has n apples and wants to divide them equally between B and C, but he doesn’t have a knife. The fruit cannot be cut, only whole apples are given. There are two sizes of apples, 100g and 200g. Given the apples owned by A, ask if they can be divided equally between B and C.

Water question, but there is a pitfall,

The first thing that is easy to think of is to change the weight of each apple to 1 or 2. After adding up the weight of all the apples, if it is an odd number , then it cannot be divided equally, otherwise it can be divided equally.

When A only has one apple, it cannot be divided equally. This is not a pitfall. It is easy to think of it. If you don’t think of it, you will get the wrong answer.

A big pitfall: when n is an odd number and they are all 200-sized apples, they cannot be divided equally! This is a huge pitfall. Many people didn’t expect it. I only discovered this problem after I was hacked. Some people have hacked others more than ten times with this. . . . The score was abruptly increased by more than a thousand points. . I have to say it’s a powerful tool for scoring points!

#include <iostream>#include <cstdio>using namespace std;int w[111];int main(){    bool s=true;    int n;    int ans=0;    scanf("%d",&n);    for(int i=0;i<n;i++)    {        scanf("%d",&w[i]);        w[i]/=100;        ans+=w[i];        if(w[i]==1)            s=false;    }    if((n%2==1)&&s)    {        printf("NO\n");        return 0;    }    if(n==1)    {        printf("NO\n");        return 0;    }    if(ans%2==0)        printf("YES\n");    else        printf("NO\n");    return 0;}